Acoustic data will be derived from utterances of children recorded in their homes at two week intervals over the period from birth to five years of age. Sound spectrograms and computer-implemented Fourier analyses and waveform measurements will be used to derive formant frequency patterns for both vowels and consonants, burst frequencies for stop consonants, durations of phonetic segments and words and fundamental frequency contours. We will also use psychoacoustic tests when appropriate to assess the functional value acoustic events as cues to phonetic and phonologic contrasts. We will in particular address the following questions: (1) the role of duration and formant frequency pattern as independent cues for vowels in English - does the child acquire the phonetic features, across all members of a phonetic class or does the child acquire individual phonetic elements? (2) syntactically conditioned word duration; (3) the status of "invarient" cues that include stop bursts versus encoded format frequency transitions to see if either cue can be regarded as "primary"; (4) the start of word acquisition with reference to the gradual development of phonetic ability in the child.